How to Destroy Prions and Proven Inactivation Methods

Prions resist nearly every sterilization method that reliably kills bacteria, viruses, and fungi. They are misfolded proteins, not living organisms, so they have no DNA or RNA to damage and no metabolism to disrupt. Destroying them requires physically unfolding or chemically dismantling the protein itself, which demands conditions far harsher than standard disinfection. Several methods can dramatically reduce prion infectivity, but the specifics matter enormously: the wrong concentration, temperature, or contact time can leave infectious material behind.

Why Prions Are So Difficult to Destroy

A prion is a misfolded version of a normal brain protein. Once it adopts its abnormal shape, it becomes extraordinarily stable. The misfolded form resists digestion by enzymes that would easily chew through most proteins, stays infectious after exposure to chemicals that destroy conventional pathogens, and tolerates heat that would sterilize a surgical suite many times over. This durability comes from the protein’s tightly packed, beta-sheet-rich structure, which essentially armors it against the forces that unravel ordinary proteins.

Making matters worse, different prion strains have different levels of toughness. When three strains (BSE, RML, and 22L) were heated at 98°C for two hours, the results were dramatically unequal. The RML strain lost six to seven orders of magnitude of infectivity, the 22L strain lost about five, and BSE showed little to no reduction in infectivity at all.¹ This strain-dependent variation means a method that works well against one prion disease might fail against another, and it is one reason why decontamination protocols tend to be aggressive by default.

Heat Alone Is Not Enough

Autoclaving is the standard method for sterilizing surgical instruments and laboratory equipment. For bacteria and viruses, a typical autoclave cycle of 121°C for 15 to 30 minutes is overkill. For prions, even much higher temperatures can fall short. Prion infectivity has been shown to survive autoclaving at 132 to 138°C, and counterintuitively, the effectiveness of autoclaving sometimes declines as the temperature increases.² The small subpopulations that survive a first autoclave cycle are not eliminated by simply running the cycle again; they appear to acquire characteristics that make them even harder to kill.

Research using a sensitive amplification assay has confirmed that prion signals persist in samples autoclaved at temperatures below 150°C, and mice exposed to those samples still developed disease.³ The practical takeaway is that heat-only sterilization is unreliable against prions unless combined with chemical treatment. Current guidelines from the WHO and CDC reflect this by recommending combined approaches rather than autoclaving alone.

Dry heat behaves differently from steam autoclaving. Comparative studies across five strains of transmissible spongiform encephalopathy found that dry heat inactivation did not show the same strain-dependent differences seen with wet heat.⁴ However, dry heat at practical temperatures is still not considered a stand-alone solution, because even when it reduces infectivity, it does not reliably eliminate it across all strains and conditions.

Chemical Methods That Actually Work

Two chemicals have the strongest track record for prion decontamination: sodium hydroxide (NaOH, or lye) and sodium hypochlorite (household bleach). Both attack the protein structure aggressively enough to unfold prions, but the details of concentration and contact time are critical.

Sodium Hydroxide

A concentration of 1 to 2 normal (1N to 2N) NaOH is the standard recommendation for surfaces and equipment. At 0.1 molar NaOH, a 15-minute treatment reduced detectable prion protein by roughly 3.5 to 4 log units, and adding a detergent during a longer soak pushed the reduction beyond the detection limit of the assay.⁵ For environmental contamination, such as farm soil where chronic wasting disease prions may linger, a 2N NaOH solution mixed into soil at a 1-to-5 ratio produced a large decrease in infectivity, on the order of a hundredfold or more.⁶

NaOH is corrosive enough to damage certain instruments and surfaces, which limits where you can use it. It also works better at warmer temperatures and with longer contact times. The addition of a detergent appears to help the chemical reach prion protein that might otherwise be shielded inside aggregates or adhered tightly to a surface.

Sodium Hypochlorite (Bleach)

Bleach is cheap, widely available, and genuinely effective against prions when used at sufficient concentration and contact time. For chronic wasting disease prions on stainless steel surfaces and in brain homogenate solutions, a five-minute soak in a 40% dilution of standard household bleach (roughly 2 to 2.5% available chlorine) eliminated all detectable seeding activity.⁷ For human Creutzfeldt-Jakob disease prions, research has mapped out more precise thresholds across multiple subtypes: 50% bleach for one minute, 20% bleach for five minutes, or 10% bleach for thirty minutes each completely removed all detectable seeding activity, achieving average log reductions between roughly 3.5 and 7.5 depending on the subtype and conditions.⁸

Bleach does have real limitations. It failed to inactivate CWD seeding activity in solid tissue samples, meaning intact brain tissue or other dense biological material cannot simply be soaked in bleach and considered safe.⁷ It is also corrosive to metals and can degrade rubber and plastics, which makes it impractical for many delicate surgical instruments. And its effectiveness drops when organic matter is present, because chlorine reacts with proteins and fats before it reaches the prions.

Formic Acid in the Laboratory

Formic acid occupies a specific niche: it is the standard treatment for brain tissue samples in neuropathology labs where prion diseases like CJD are suspected. Immersing tissue in concentrated formic acid (usually 96% or higher) for an hour is common practice before the tissue is processed for microscopic examination. This treatment has been shown to reduce infectivity by roughly 4.4 log units for variant CJD and about 5 log units for sporadic CJD, based on incubation-time studies in sensitive mouse models.⁹ Those reductions are major, though researchers still detected residual infectivity in some samples, meaning formic acid is a powerful risk-reduction tool rather than a guaranteed sterilizer.

There is a trade-off worth noting for pathologists. Formic acid pretreatment can interfere with certain diagnostic stains. In breast cancer patients whose tissue is treated with formic acid because of suspected prion disease, the treatment can lower scores on the HercepTest, which is used to determine eligibility for targeted therapy.¹⁰ This is a narrow clinical scenario, but it illustrates how prion safety protocols can ripple into other areas of medical care.

The Surgical Instrument Problem

Prion contamination of surgical instruments is one of the most concerning real-world scenarios. Standard hospital sterilization, designed around bacteria and viruses, does not reliably eliminate prions. The CDC and WHO have both acknowledged that standard decontamination and sterilization procedures may be insufficient to completely remove infectivity from prion-contaminated instruments.¹¹

Part of the difficulty is how stubbornly prions stick to stainless steel. Prion protein adsorbs tightly to metal surfaces, and the composition of the steel matters. Stainless steel containing nickel and molybdenum, common in surgical instruments, binds prion protein more efficiently and transmits infection to a greater degree than steel without those elements.¹² Once prions adhere, they are difficult to dislodge even with aggressive chemical treatment.

Timing also plays a role. The longer instruments sit after contamination, the worse the problem gets. Allowing contaminated surfaces to dry increases both protein and prion amyloid adsorption and reduces how well cleaning chemicals work afterward.¹³ Keeping instruments moist after use significantly reduces how tightly prions bind, which is why current best-practice guidelines recommend that potentially contaminated instruments be kept wet or placed in humidity-retention bags until they can be reprocessed.¹⁴

For high-risk neurosurgical cases where prion disease is suspected, some guidelines recommend single-use instruments or quarantining reusable instruments until a diagnosis is confirmed. If prion disease is confirmed, the instruments are destroyed rather than reprocessed.

Gaseous and Enzymatic Approaches

Chemicals like NaOH and bleach are effective but corrosive, which has driven interest in gentler alternatives that could be used on sensitive equipment.

Vaporized hydrogen peroxide is one such option. In its gaseous form, hydrogen peroxide can inactivate prions on stainless steel, whereas liquid hydrogen peroxide is not effective. Mice implanted with prion-contaminated steel wires treated with vaporized hydrogen peroxide developed disease later than those implanted with untreated contaminated wires, indicating reduced infectivity.¹⁵ The mechanism appears to involve protein unfolding and increased vulnerability to enzymatic digestion afterward.¹⁶ Because vaporized hydrogen peroxide is already used in low-temperature sterilization systems for heat-sensitive medical devices, integrating prion decontamination into existing workflows is plausible.

Enzymatic approaches, using proteases to digest the misfolded protein, also show promise but with caveats. Common digestive enzymes like trypsin and pepsin are ineffective against prions. Subtilisin-type proteases (including Proteinase K, the enzyme most widely used in prion research) can break down prion protein, but only when combined with heat above 100°C and detergent to loosen the aggregates first.¹⁷ Without those harsh pre-treatments, the prion aggregates are too tightly packed for enzymes to access. So enzymatic methods are typically used as a component of a multi-step process rather than a stand-alone solution.

Prions in the Environment

Prion contamination is not just a hospital or laboratory concern. In wildlife diseases like chronic wasting disease in deer and elk, prions shed into the environment through saliva, urine, feces, and decomposing carcasses. Once in the soil, they can persist for years and remain infectious. Prion protein binds avidly to clay minerals, especially montmorillonite, and this binding actually increases oral disease transmission rather than neutralizing the prions.¹⁸ The interaction between prion protein and mineral surfaces is strong enough that desorbing the protein is difficult, yet the bound prions remain infectious and bioavailable.¹⁹

This environmental persistence creates a self-sustaining cycle for diseases like CWD: infected animals shed prions into pastures and water sources, the prions bind to soil and resist degradation, and naive animals pick them up during grazing. Treating contaminated soil with 2N NaOH can achieve meaningful reductions, as noted earlier, but decontaminating hundreds of acres of rangeland is a different challenge entirely from cleaning a set of surgical tools.

Water Treatment and Ozone

The question of prions in water is particularly relevant for rendering plants, slaughterhouses, and communities downstream from areas where CWD is endemic. Ozone, already used in municipal water treatment for other pathogens, shows real efficacy against prions in water. In laboratory conditions using clean buffered water, ozone achieved measurable prion inactivation that varied with pH and temperature.²⁰

Real-world waters are messier. In rendering plant wastewater, raw effluent consumed ozone instantly before it could act on prions, but after primary treatment to remove gross organic matter, ozone achieved greater than four-log inactivation within five minutes. Municipal secondary-treated wastewater showed similar results at a higher ozone dose.²¹ The practical lesson is that ozone can serve as a final barrier for prion-contaminated water, but only after conventional treatment has first removed enough organic material for the ozone to reach the prions.

Incineration and Alkaline Hydrolysis for Disposal

When the goal is not to clean a surface but to permanently dispose of prion-contaminated material, incineration and alkaline hydrolysis are the two main options.

Incineration at high temperatures is considered the most definitive approach. European food safety regulations require that category 1 animal by-products (the highest-risk category, including material from animals suspected of prion disease) be exposed to combustion gases of at least 850°C for two seconds or 1100°C for 0.2 seconds.²² These temperatures are high enough to break apart any organic molecule, prion included. The challenge is verifying that every piece of material actually reaches those conditions in an industrial-scale incinerator.

Alkaline hydrolysis offers an alternative that is especially practical for the livestock industry. This process uses a concentrated alkali solution (typically sodium or potassium hydroxide) under heat and pressure to dissolve biological tissue entirely, reducing carcasses to a sterile liquid and mineral residue. In testing against mouse-adapted scrapie, none of the mice exposed to alkaline-hydrolysis-treated material developed disease, validating its ability to inactivate prion infectivity completely.²³ The method has been proposed as a practical alternative to incineration, landfill burial, and conventional rendering for disposing of potentially prion-infected carcasses and slaughterhouse waste.

What Does Not Work

Knowing what fails is just as important as knowing what works, because many standard sterilization methods that people assume are universal give a false sense of security with prions.

Ionizing radiation, including gamma rays at doses that would sterilize almost anything biological, is remarkably ineffective. Even at 50 kilograys, a dose hundreds of times higher than what is used for food irradiation, infectivity from kuru, CJD, and scrapie dropped by only about 90%. At 200 kilograys, the reduction was still only between 90% and 99.9%.²⁴ For context, radiation sterilization of medical devices typically uses 25 kilograys. Prions survive because radiation damages nucleic acids, and prions have none; the protein itself is a small enough target that radiation simply misses most of it.

Standard autoclaving at 121°C, formaldehyde, ethanol, ultraviolet light, boiling, and most common hospital disinfectants are all insufficient on their own. This is not a theoretical concern. Documented cases of iatrogenic prion transmission, where patients acquired CJD from contaminated surgical instruments, neurosurgical depth electrodes, or human-derived hormones, occurred precisely because standard sterilization was assumed to be adequate.

How Prion Inactivation Is Measured

Evaluating whether a decontamination method actually works against prions is itself a difficult problem. For decades, the gold standard was the animal bioassay: treat the contaminated material, inject it into the brains of laboratory mice or hamsters, and wait months to years to see if they develop disease. This is sensitive and definitive, but painfully slow and expensive.

A faster alternative called RT-QuIC (real-time quaking-induced conversion) has become widely adopted. This assay detects whether a sample contains prion “seeds” capable of triggering misfolding of normal protein in a test tube. Head-to-head comparisons show that RT-QuIC sensitivity is roughly comparable to that of animal bioassays for quantifying prion seeding activity.²⁵ Importantly, when both methods are applied to the same decontaminated samples, their results agree on whether residual infectivity remains.²⁶ RT-QuIC has also been increasingly used to evaluate disinfectants and potential therapeutics, giving researchers a practical way to screen new decontamination approaches without years-long animal studies.²⁷

Cold Atmospheric Plasma and Other Emerging Methods

The search for non-corrosive, instrument-friendly prion decontamination methods has led researchers toward some unconventional technologies. Cold atmospheric plasma, which generates reactive oxygen and nitrogen species from air or other gases at room temperature, is among the most promising. Studies using various gas plasma instruments derived from air, nitrogen, oxygen, argon, and gas mixtures have demonstrated the ability to inactivate scrapie prions.²⁸

In one practical test, cold atmospheric plasma was used as a final step in reprocessing flexible endoscopes, which are especially challenging to decontaminate because of their narrow channels and sensitivity to harsh chemicals. After a standard enzymatic pre-wash, plasma-activated gas effluents prevented prion transmission according to a cell-based infectivity assay.²⁹ The appeal of plasma is clear: it works at room temperature, leaves no chemical residue, and does not corrode metal or degrade plastics. Optimizing delivery, particularly getting the reactive species deep into instrument lumens, remains the main engineering hurdle before widespread clinical adoption.